If the 1980s GISA is an integral part of the interdecadal climate cycle shown in Figure 1, it is conceivable that it too could have been partly generated by large runoffs in the western Arctic during the mid-1980s. Figure 3a shows that during the mid-1980s the Mackenzie River runoff was indeed slightly above average. This led to below-average salinities on the Beaufort shelf to the north of the Mackenzie delta (Figure 3b) and, for the period 1984-1986, to above-average areal sea-ice anomalies (Figure 3c) in the western Arctic subregion B1 (identified in Figure 4). Heavy ice conditions in the Beaufort Sea can also be seen at this time in the ice atlas of Mysak and Wang (1991) (see also Figure 4b

FIGURE 3

(a) Annual Mackenzie River runoff at the Arctic Red River (a city on the Mackenzie River) for 1973-1989 (data courtesy of R. Lawford). (b) Salinity at I m depth over the southeastern Beaufort Sea continental shelf (in subregion B1, shown in Figure 4) in July, August, and September for 1950-1987 (data from Fissel and Melling, 1990). (c) Smoothed areal sea-ice anomalies in the Beaufort Sea subregion B for 1953-1988. (From Mysak and Power, 1992; reprinted with permission of the Canadian Meteorological and Oceanographic Society.) In deriving the time series in (c), the monthly areal sea-ice-extent anomalies were low-pass filtered so as to remove all fluctuations with periods shorter than 30 months.

FIGURE 4

Subregions used in the cross-correlation analysis of low-pass filtered sea-ice anomalies derived from ice-concentration data given on a 1°X 1° (latitude) grid (developed by Walsh and Johnson, 1979) for 1953-1988. (Adapted from Mysak and Power, 1992; reprinted with permission of the Canadian Meteorological and Oceanographic Society.) In this paper cross-correlation results are presented only for the subregions labeled B1, B2. B3, B4, D1, D2, and D3. The dashed line denotes the 200 m isobath.

in Mysak and Power, 1992). It is also interesting to note the sharp ice-anomaly peak in 1975, evident on Figure 3, which presumably occurred in response to the high runoff and low salinities in 1974; similarly, we note the sequence of low ice anomalies from 1978 to 1982, which correspond to low runoff and high shelf salinities at that time. Figure 3c also indicates the large ice anomalies from 1964 to 1967, which, as was pointed out by M3, were likely due to the very large runoffs in 1964-1966. (Mysak and Power (1992) present evidence that shows that local winds may also have played a role in producing the Beaufort Sea ice anomalies.)

It has often been suggested by critics of the interdecadal-cycle theory characterized by Figure 1 that runoff from the Siberian rivers, which in total is 4 to 5 times that of the Mackenzie, should contribute substantially to sea-ice anomalies in the Arctic and subsequently in the Greenland and Iceland seas. Here we counter (as does M3, in more detail) that, because the Eurasian shelf is very wide and shallow, this runoff gets well mixed there with the central Arctic Ocean waters that also flow onto the shelf. Such mixing takes place mainly through tides and eddies in this region; also, convective overturning on the shelf mixes the surface runoff with the deeper shelf water. Fluctuations in the Siberian river flow thus have little direct bearing on the creation of sea-ice anomalies in the central Arctic. A similar conclu-



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